D. polymorpha, the Zebra mussel, has just recently been introduced to North America. D. polymorpha was first discovered in June, 1988 in Lake St. Clair and is thought to have been introduced into the region in 1986 by fresh water ballast discharge from an ocean-going ship. Since its introduction, D. polymorpha has spread rapidly throughout Lake Erie and into western Lake Ontario. Scattered populations have now been found in all five Great Lakes. Native to the Black and Caspian Seas, D. polymorpha rapidly spread throughout Europe and the Soviet Union during the past two centuries and is expected to soon be a major macrofouling pest in fresh waters throughout the United States.
Common to bivalve molluscs, fouling by Zebra mussel occurs primarily as a result of larvae transport into plant systems by water currents, settlement of the larvae in low flow areas, and subsequent growth of the organism to sizes large enough to impair system operation.
Zebra mussel larvae and juveniles aggressively attach to all types of hard surfaces including intake structures, screens, pipes, and other mussel shells, to form dense thick layers of mussel accumulations. Pipeline surfaces can be entirely encrusted by Zebra mussel shells, impeding flow and accelerating corrosion. Clusters and massive mats of mussel shells can break off and become entrained back in the fluid flow, causing equipment plugging and additional fouling problems.
The literature is replete with summaries of the problems occasioned by Zebra mussel fouling of surfaces in contact with industrial process waters, particularly industrial cooling waters. Two such summaries are: "Macrofouling Control", by M. G. Trulear et al., Nalco Reprint No. 533, December 1990., and "Zebra Mollusks: A Danger of a Different Shape", Bretz, E., Electrical World December 1990, pages 72-74. The disclosure of these articles is incorporated herein by reference.